The present disclosure relates to bonding substrates, and particularly, to a method of bonding substrates while minimizing substrate warping, a vacuum carrier for effecting the same, and a structure for implementing the same.
Substrate warping poses a challenge for the attachment of a semiconductor chip to a packaging substrate. A large substrate warp at reflow is a cause for unreliable C4 bonding, leading to potential non-wets or unequal C4 solder heights. Even for a population of substrates having a nominal mean warp, there is usually a large variation (sigma) in the warp which can be a problem during bond and assembly. The thermal warp, i.e., the change in warp with temperature, is another undesirable problem for bond and assembly. A large thermal warp means that the packaging substrate changes shape during the critical cool down period after the reflow of solder balls. Such change in the shape of the solder balls could lead to defects in the solder ball joints such as hot tears.